In nuclear reactor plants ionic impurities are normally removed from the water in the reactor primary circuit with the aid of ion-exchange filters containing ion-exchange resin. The impurities consist mainly of corrosion products from the construction material in the primary circuit, such as ions of or containing iron, manganese and chromium, which have become radioactive when the water containing these corrosion products has passed the reactor core. The water in the primary circuit may also contain impurities in the form of fission products of the reactor fuel which have leaked out into the water. Even water outside the primary circuit, such as water from floor drains and discharge pipes, is normally subjected to purification in filters with ion-exchange resins to remove radioactive impurities.
An ion-exchange filter of the kind stated above often comprises a chamber containing a plurality of filter elements, each one consisting of a support matrix permeable to liquid and of a layer of small-sized particles of an ion-exchange resin (precoatfilter), which layer is generated on the support matrix in the chamber. The layer of the ion-exchange resin can be applied on the support matrix by arranging the filter in a liquid circulation system and supplying a suspension of the ion-exchange resin to the liquid while the liquid is circulated in the circulation system.
When applying a layer of ion-exchange resin in an ion-exchange filter, there is normally used a mixture of powdered cation exchange resin and powdered anion exchange resin in the form of a suspension in water. Usually, the mixing of the cation exchange resin and the anion exchange resin is carried out while at the same time the suspension in the water is effected while using a tank which is provided with a rotatable agitator, for example a turbine agitator. This process is time-wasting and produces a result which is difficult or almost impossible to reproduce. The reason for this is primarily the tendency to agglomeration of particles which occurs and which is due to the great electrostatic charge of the particles. When the suspension is then supplied to circulating water in a circulation system, in which the ion-exchange filter is arranged, a dilution of the suspension takes place, which may lead to the particles of the ion-exchange resin not becoming homogeneously distributed in the diluted product and, as a consequence thereof, to the coating layer of the particles on the support matrix not being uniform. Also, if the manufacture of the suspension starts from a mixed product of the ion-exchange resin, the same difficulties exist in achieving coating layers on the support matrix having reproducible properties.